JP3781198B2 - Image forming apparatus - Google Patents

Description

【００２７】
なお前述の実験に使用した定着器37の仕様ならびに現像器33に用いられる現像剤には次の仕様のものが使用されている。
【００２８】

【００２９】
【発明の効果】
本発明により、記録線密度の切換により感光体線速度が変化しても常に一定した感光体帯電電位が得られることとなり、その結果かぶりやキャリアの付着がなく高品位の画像を記録出来る画像形成装置が提供されることとなった。
【図面の簡単な説明】
【図１】本発明の画像形成装置の断面構成図。
【図２】レーザ書込み部の平面図。
【図３】記録線密度の切換にかかわる制御回路図。
【図４】感光体ドラムの帯電回路図。
【図５】帯電電位とグリッド電圧の関係を示すグラフ。
【符号の説明】
10 画像読取り部
20 レーザ書込み部
30 画像形成部
31 帯電器
32 感光体ドラム
33 現像器
34 転写器
35 分離器
36 搬送ベルト
37 定着器
37Ａ 上ローラ
37Ｂ 下ローラ
40 給紙部
41 給紙カセット[0001]
[Industrial application fields]
The present invention relates to an image forming apparatus including a scorotron charging device and a laser beam exposure device.
[0002]
[Prior art]
In an electrostatic image forming apparatus equipped with an exposure device using a laser beam, the screen of the electrostatic latent image formed on the photosensitive member is formed by combining the main scanning by the laser beam and the sub-scanning accompanying the movement of the photosensitive member. Is done.
[0003]
The electrostatic latent image has a recording linear density by main scanning (reducing the linear velocity of a polygon mirror or a galvanometer mirror) by reducing the speed of the sub-scanning, that is, reducing the rotation speed when the photosensitive drum is a drum. Can be recorded closely. Accordingly, if the moving speed of the photosensitive member and the linear speed of the polygon mirror or galvano mirror can be switched to the low speed side, a high-quality image with a higher pixel density can be obtained.
[0004]
[Problems to be solved by the invention]
However, conventionally, even if the moving speed is switched, the photosensitive member is given a potential by a constant charging voltage. Therefore, if the charging potential is set to a value that is an optimum condition at a low speed of the photosensitive member, the photosensitive member is at a high speed of the photosensitive member As the current value per unit area on the surface of the photoreceptor decreases, the charging potential decreases. As a result, when the development bias voltage is constant, “fogging” occurs in an image that has undergone reversal development.
[0005]
Also, if the charging potential is set to a value that is an optimum condition at a high speed of the photosensitive member, the charging potential becomes excessively high due to an increase in the current value per unit area on the surface of the photosensitive member at a low speed of the photosensitive member. Is constant, the carrier in the developer may adhere to the photosensitive member and the photosensitive surface may be damaged during cleaning.
[0006]
An object of the present invention is to provide an image forming apparatus in which the charged potential per unit area can always be kept constant even if the moving speed of the photosensitive member changes as a result of solving and improving this point. is there.
[0007]
[Means for Solving the Problems]
The object is to expose a photoconductor, a scorotron charging device having a charging wire and a grid for charging the photoconductor, a semiconductor laser and a polygon mirror, and scanning the photoconductor with laser light. A laser writing unit for forming an electrostatic latent image, and switching the recording linear density of the electrostatic latent image by switching the linear velocity of the photosensitive member and the polygon mirror. In accordance with the switching of the linear velocity of the photosensitive member and the polygon mirror for switching the linear density, the grid voltage setting of the grid is changed so as to make the charging potential of the photosensitive member constant, and the charging wire is supplied to the charging wire. This is achieved by an image forming apparatus characterized in that the supplied charging current and developing bias are not switched .
[0008]
【Example】
Embodiments of the image forming apparatus of the present invention are shown in FIGS.
[0009]
The image forming apparatus includes an image reading unit 10, a laser writing unit 20, an image forming unit 30, and a paper feeding unit 40.
[0010]
The image of the document D placed on the document table is obtained by translating the first mirror unit 11 including the illumination lamp 11A and the mirror 11B of the image reading unit 10 from the solid line to the position indicated by the broken line, and a pair of opposed mirrors. The second mirror unit 12 provided with 12A is exposed and scanned by a follow-up movement at a half speed with respect to the first mirror unit 11, and the image is formed on the image sensor 14 through the projection lens 13, and the image sensor The electric signal photoelectrically converted by 14 is temporarily stored in the memory as an image signal through image processing.
[0011]
Next, when the image signal is input to the laser writing unit 20, the laser beam generated by the semiconductor laser is rotationally scanned by the polygon mirror 22 rotated by the drive motor 21. FIG. 2 is a plan view showing the scanning optical system of the laser writing unit 20, and two beams of semiconductor lasers generated from a pair of laser units U1 and U2 arranged so that their optical axes are orthogonal to each other. Rotate the polygon mirror 22 that rotates in the direction indicated by the arrow through the cylindrical lens 27 after aligning the directions in the main scanning direction and the sub-scanning direction with the adjusting prisms P1 and P2, respectively. Projected onto the surface.
[0012]
The two projected laser beams are reflected and scanned by the movement of the rotating surface of the polygon mirror 22, and the photosensitive surface of the photosensitive drum 32 to which a charge is applied in advance by the charger 31 through the fθ lens and the cylindrical lens 28. The electrostatic latent image of the original image is formed on the photosensitive drum 32 by scanning exposure. Accordingly, an electrostatic latent image of the original image is formed on the peripheral surface of the photosensitive drum 32 by the main scanning by the laser beam and the sub-scanning accompanying the rotation of the photosensitive drum 32. This latent image is reversely developed by the toner carried by the developing sleeve 33A to which the developing bias of the developing device 33 is applied to form a toner image.
[0013]
On the other hand, the transfer paper P of a specified size is carried out from each paper feed cassette 41 loaded in the paper feed unit 40 by the operation of the carry-out roller 41A of the paper feed cassette 41 to be stored, and the image is transferred via the transport roller 43. Paper is fed toward the copy.
[0014]
The fed transfer paper P is fed to the transfer unit in synchronization with the toner image on the peripheral surface of the photosensitive drum 32 described above by the registration roller 44 and is fed to the transfer unit in synchronism with the toner image. The toner image is transferred onto the transfer paper P.
[0015]
Next, the transfer paper P is separated from the peripheral surface of the photosensitive drum 32 by the charge eliminating action of the separator 35, conveyed to the fixing device 37 via the conveying belt 36, and the toner is sandwiched between the upper roller 37A and the lower roller 37B and heated. Is transferred from the fixing device 37 via the conveying roller 38, and the discharged transfer paper P is discharged onto the tray 50 via the paper discharge roller 45.
[0016]
On the other hand, the photosensitive drum 32 from which the transfer paper P has been separated removes residual toner by a blade 39A pressed against the cleaning device 39, cleans it, and then receives a charge from the charger 31 again to enter the next image forming process.
[0017]
The apparatus switches the recording linear density of the electrostatic latent image formed on the photosensitive drum 32 from, for example, a normal 400 dpi (400 dots per inch) to a 600 dpi density by means of a switching means provided in the operation unit. Furthermore, it has a function to record high-quality images.
[0018]
The above-described switching of the recording linear density to a high density reduces the linear velocity of the photosensitive drum 32 and the polygon mirror 22 in accordance with a command from the control system shown in FIG. This is realized by appropriately changing the image forming conditions of the forming member.
[0019]
When the recording linear density is set to 400 dpi without switching, the linear velocity of the photosensitive drum and the related image forming conditions are set to the characteristic values shown in the column “400 dpi” in Table 1. And
[0020]
By switching the recording linear density from 400 dpi to 600 dpi, the linear velocity of the photosensitive drum 32 is changed from 280 mm / sec to 125 mm / sec as shown in the column of “600 dpi” in Table 1, and the rotational speed of the polygon mirror 22 is 16535 rpm. The rotation speed of the developing sleeve 33A is reduced from 250 rpm to 110 rpm, and the conveyance speed of the transfer paper P and the driving speed of the fixing device 39 are also reduced correspondingly.
[0021]
On the other hand, the charged potential of the photosensitive drum 32 is maintained at −700 V, which is the same level as before the switching of the recording linear density, that is, 400 dpi without changing even if the linear velocity is lowered.
[0022]
In the present invention, only the grid voltage is changed so that the charged potential of the photosensitive drum 32 is maintained at the same level. That is, the charger 31 is a scorotron type charger having a grid G at a position along the peripheral surface of the front photosensitive drum 32 of the charging electrode wire W as shown in FIG. The constant current power supply for charging that supplies current to the recording medium does not receive the recording linear density switching signal from the CPU (charging control unit), and the charging total current of 800 μA corresponding to the case where the recording linear density is always 400 dpi is 600 dpi. Supplied even when switched. On the other hand, in the amplifier that applies a voltage to the grid G, the charging grid voltage is lowered from −620 V (at 400 dpi) to −560 V (at 600 dpi) by a recording linear density switching signal from the CPU (charging control unit). The charging potential applied to the body drum 32 is always kept at a constant -700V.
[0023]
FIG. 5 shows the relationship between the charging potential VH corresponding to the linear velocity of the photosensitive member and the grid voltage VG. When the recording linear density is switched from 400 dpi to 600 dpi, the grid voltage VG is changed from VG1 to VG2. The charging potential per unit area of the photosensitive drum 32 can be set to a constant potential HV.
[0024]
According to the inventor's experiments, the grid voltage of the grid G be switched to the recording linear density 600dpi leave -620V and Then, the resulting photoreceptor photoreceptor potential rises to -780V from -700V Although carrier adhesion was observed, if the charging grid voltage was changed to decrease from -620V to -560V as described above, the charged potential of the photoconductor did not change and was kept constant at -700V. It has been confirmed that carrier or adhesion of images can be avoided without requiring correction of current or developing bias voltage.
[0025]
In the embodiment, the recording linear density has been described with respect to 400 dpi and 600 dpi. However, the present invention is not limited to this, and the present invention is also applicable to the case of switching to three recording linear densities.
[0026]
[Table 1]

[0027]
The following specifications are used as the specifications of the fixing device 37 used in the above-described experiment and the developer used in the developing device 33.
[0028]

[0029]
【The invention's effect】
According to the present invention, even if the photosensitive member linear velocity is changed by switching the recording linear density, a constant photosensitive member charging potential can be obtained. As a result, image formation capable of recording a high-quality image without fogging or carrier adhesion. A device was provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional configuration diagram of an image forming apparatus of the present invention.
FIG. 2 is a plan view of a laser writing unit.
FIG. 3 is a control circuit diagram relating to switching of recording linear density.
FIG. 4 is a charging circuit diagram of a photosensitive drum.
FIG. 5 is a graph showing a relationship between a charging potential and a grid voltage.
[Explanation of symbols]
10 Image reader
20 Laser writing section
30 Image forming section
31 Charger
32 Photosensitive drum
33 Developer
34 Transfer device
35 Separator
36 Conveyor belt
37 Fuser
37A Upper roller
37B Lower roller
40 Feeder
41 Paper cassette

Claims (1)

A photosensitive member, a scorotron charging device for charging the photosensitive member having a charging wire and a grid, and a semiconductor laser and a polygon mirror for scanning and exposing the photosensitive member by scanning a laser beam for static exposure. An image forming apparatus having a laser writing unit for forming an electrostatic latent image, and switching a recording linear density of the electrostatic latent image by switching a linear velocity of the photosensitive member and the polygon mirror;
In accordance with the switching of the linear velocity of the photosensitive member and the polygon mirror for switching the recording linear density, the grid voltage setting of the grid is changed so as to make the charging potential of the photosensitive member constant, and the charging is performed. An image forming apparatus characterized in that a charging total current supplied to a wire and a developing bias are not switched .

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